We propose to work out a method for isolation of protein structural genes from higher organisms. It involves limited exonuclease digestion of DNA, hybridization with messenger RNA corresponding to the desired gene, and separation of DNA-RNA hybrids from other DNA. The DNA which was hybridized will be replicated in Escherichia coli to produce large quantities. This method will be used to isolate the silk fibroin gene with the DNA sequences adjacent to it in the genome of the silkworm, Bombyx mori. We will determine whether the gene can be transcribed and RNA from it translated in bacteria. We will map the DNA adjoining the fibroin gene by restriction endonuclease cleavage and examine if for repeated sequences by its rate of annealing. If any reiterated segments are found, their association with tissue-specific transcription will be tested. BIBLIOGRAPHIC REFERENCES: The Prospects for Gene Therapy in Humans. John F. Morrow. Ann. N.Y. Acad. Sci. 265, 13-21 (1976). In press: Plasmids containing silk fibroin gene sequences. John F. Morrow, John M. Wozney & Argiris Efstratiadis. In Impact of Recombinant Molecules on Science and Society, Raven Press, New York, 1976.